update known variables (microsoft#250723)

Author: aeschli

build/lib/stylelint/vscode-known-variables.json

@@ -344,7 +344,6 @@
 		"--vscode-editorWidget-foreground",
 		"--vscode-editorWidget-resizeBorder",
 		"--vscode-errorForeground",
-		"--vscode-extension-border",
 		"--vscode-extensionBadge-remoteBackground",
 		"--vscode-extensionBadge-remoteForeground",
 		"--vscode-extensionButton-background",
@@ -573,7 +572,6 @@
 		"--vscode-pickerGroup-border",
 		"--vscode-pickerGroup-foreground",
 		"--vscode-ports-iconRunningProcessForeground",
-		"--vscode-preferences-sashBorder",
 		"--vscode-problemsErrorIcon-foreground",
 		"--vscode-problemsInfoIcon-foreground",
 		"--vscode-problemsWarningIcon-foreground",